This invention relates to a silicon carbide sintered article and to a method for making the same. The silicon carbide sintered article of the present invention is suitable for a shelf inside a rapid firing furnace.
Silicon carbide ceramic is excellent in heat resistance and fire resistance and has various industrial applications. Silicon carbide ceramic is used as material for, for example, a shelf to hold ceramics in a kiln or in a furnace and a central tube in a furnace to fire semiconductors.
A prior art method for making a silicon-carbide ceramic includes the steps of: adding carbon powders and a binder to .alpha.-silicon powders; mixing the mixture; forming the resulting mixture into a compact; and firing the compact under a silicon atmosphere. A silicon-carbide ceramic thus obtained includes grains of .alpha.-silicon carbide resulting from the starting compound and grains of .beta.-silicon carbide dispersed around the grains of the .alpha.-form. The .beta.-silicon carbide is formed by the reaction of carbon and silicon. Pores which were made during the reaction are filled by silicon.
FIG. 2 is a scanning electron microscope photograph of a silicon-carbide sintered article thus obtained. The photograph has the same magnification as the photograph in FIG. 1. The white part in FIG. 2 shows grains of .alpha.-silicon carbide.
An alternative prior art method for making a silicon-carbide ceramic includes steps of adding a binder and ingredients for forming glass to .alpha.-silicon carbide powders; mixing the mixture; forming the resulting mixture into a compact; and firing the compact under an oxidizing atmosphere.
These methods give thick ceramics, and such thick ceramics are not suitable for certain applications. A thick ceramic tends to have a large heat capacitance, thus upon heating heat distribution generated in the ceramic decreases its thermal shock resistance. Moreover, a thick ceramic is susceptible to having pores inside, thus reducing its oxidation resistance.
Prior act silicon-carbide ceramics do not include any special antioxidant. Such a ceramic is prone likely to have limited oxidation resistance.
One approach to make a thin silicon-carbide ceramic is to make .alpha.-silicon carbide powders finer. This approach, however, increases the cost of making the ceramic. Without making the powders finer, a thin compact does not have sufficient mechanical strength so that it cannot maintain its shape during firing.